The response of normal and malignant estrogen target tissues to estradiol is determined by the concentration and retention time of nuclear receptor estrogen complexes (RE2). Vitamin B6 inhibits nuclear binding of RE2 by interfering with the cytoplasmic activation and nuclear retention reactions in vitro. It is the purpose of this study to further characterize these reactions and to determine if similar events can be observed in vivo using normal rat uterus and DMBA-induced mammary tumors. Furthermore, in vitro physico-chemical analysis of estrogen receptor and anti-estrogen receptor states in the cytoplasm and nuclear cell fractions will be carried out in the presence and absence of specific chemical probes.